Radiant heating systems include a heater that is thermally coupled to radiators in different zones of a building. In a conventional radiant heating system, radiators are positioned in rooms in a residential structure and are operatively coupled to one or more boilers. Hot water from the boiler is fed to the radiators to radiantly heat the respective rooms. In most heating systems, each radiator is operatively connected to a respective valve that can be opened and closed to control the flow of hot water into the radiator and thereby control the temperature of the room. In many modern systems, the radiator valves are controlled by thermostatic actuators that selectively open and close the valve based on the environmental temperature in the respective room.
Traditional thermostatic valves operate passively. A thermally responsive element, such as a bellows, a plug of wax, a metallic coil, etc., expands and contracts and drives movement of a pin to open and close the valve. No energy other than changes in environmental temperature is required to open and close the valve. However, because conventional thermostatic actuators are only passively responsive to changes in environmental temperature, they are not suitable for centralized system control.
To provide some degree of centralized control in a zoned radiant heating system, electronic thermostatic valve actuators can be used instead of passive thermostatic actuators. Unlike passive thermostatic actuators, electronic actuators use motorized drivers to selectively open and close the valve and thus must draw power from a power supply to maintain or adjust the temperature in a room. Although the set point temperature of an electronic actuator can be adjusted from a central control module, providing power requires either running wires from an external power supply to the actuator or including in the actuator an onboard power supply that must be recharged or replaced as it is drawn down.